1. Field of the Invention
The present invention relates to a system for controlling total power consumption of a plurality of apparatuses, and a control method thereof.
2. Description of the Related Art
There is a need for setting an upper limit of total power consumption of OA equipments which are operating in an office. Especially, such a need has arisen in large-scale offices where there are a large number of electrophotographic image forming apparatuses such as MFPs (Multi Functional Printers), printers, and FAX (facsimile) apparatuses operating. Therefore, there is a need to reduce power consumption, or a limited power supply capability for a power supply equipment.
Conventionally, there is an example in which a total power consumption amount of a large number of apparatuses is estimated, and power supplies of these apparatuses are controlled not to exceed an upper limit value (see Japanese Patent Laid-Open No. 2006-227691). In this example, a server calculates a total power consumption amount of the respective apparatuses, and turns off power supplies of apparatuses with lower operation rates when the upper limit value is exceeded.
On the other hand, an electrophotography image forming apparatus uses a heater to form an image. In order to fix toner powder, which is electrostatically attracted on a print sheet, on the print sheet, the toner is attached to the print sheet under pressure by a high-temperature roller. In order to set the roller to a high temperature, a heater in an MFP consumes an electric power of several hundred to several thousand W (watt). An occupation ratio of power consumption of the heater to that of the overall image forming apparatus is high (for example, 70% to 90%). This ratio depends on the specifications of image forming apparatuses. That is, an apparatus with a higher print speed requires a larger amount of power to be consumed, and the occupation ratio of power consumption of the heater to that of the overall apparatus tends to be higher. Therefore, in an environment in which heaters of a plurality of image forming apparatuses are operating at the same time, a total power consumption amount may assume a large value.
In the heater control, the power supply ON/OFF state of the heater is controlled so as to maintain a target temperature, which is set in advance. As the simplest example of the control method, when the value of a temperature sensor exceeds a given value, the heater is set in a power supply OFF state; when it falls below the given value, the heater is set in a power supply ON state. In a typical MFP, a switching cycle between the power supply ON and OFF states is on the order of several sec to several ten sec, and the MFP consumes an electric power only in the power supply ON state. An average power consumption amount per cycle can be defined by (a power consumption amount in the heater power supply ON state)×(a duty ratio of a current to be supplied to the heater). This duty ratio is a ratio of a power supply ON time period to one switching cycle between the power supply ON and OFF states of the heater. Note that a required electric power tends to be higher as the apparatus requires a higher print speed. This is because the apparatus with a high print speed has a high conveyance speed of a print sheet, and a heat application time period when the heater applies heat to the print sheet to fix an image is short. The required electric power also varies depending on the thickness of a print sheet. Since a heat absorption amount increases with increasing thickness of a print sheet, the required electric power increases.
The duty ratio which decides the average power consumption amount of the MFP depends on the target temperature and current temperature of the heater. Furthermore, the target temperature varies depending on job execution states. Control states of the MFP are classified into, for example, the following four states: a “power supply OFF” state in which the electric power to be supplied to the heater is completely cut off; a “standby” state in which the power supply ON/OFF state of the heater is controlled so that the heater falls within a given temperature range; a “heating” state in which the heater is set in a normally power supply ON state; and a “printing” state of job data.
In a printing apparatus in which the heater control state changes like the aforementioned four states, when the power supply ON/OFF state of the heater is uniquely controlled like in Japanese Patent Laid-Open No. 2006-227691, a long waiting time period from when the user inputs a print instruction until a print operation is started is often required. The above literature does not consider any change in power consumption of the apparatus depending on the apparatus state. For this reason, although the total power consumption amount exceeds a power supply capability in an office, the number of apparatuses in a power supply ON state increases in some cases.